U.S. patent application number 10/247797 was filed with the patent office on 2003-05-15 for portable electronic ballast.
Invention is credited to Nerone, Louis R..
Application Number | 20030090217 10/247797 |
Document ID | / |
Family ID | 26938913 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030090217 |
Kind Code |
A1 |
Nerone, Louis R. |
May 15, 2003 |
Portable electronic ballast
Abstract
A portable lighting ballast includes first and second
transistors 20, 22 for converting direct current from a voltage
source 16 into alternating current to operate a lamp 10. The lamp
has an ignition voltage that is significantly higher than the
voltage that the source 16 produces. The battery is a typical 6
volt cell or a combined source of 4 "D" cells, also producing six
volts. The ignition voltage of the lamp 10 is approximately 600 V.
A transformer 34 boosts the alternating current signal from the
transistors 20, 22 to an amplitude sufficient to ignite the lamp
10. The transformer 34 boosts the signal to 1.2 kV. After lamp
ignition, the transformer settles the voltage to a steady state
value.
Inventors: |
Nerone, Louis R.;
(Brecksville, OH) |
Correspondence
Address: |
Timothy E. Nauman, Esq.
Fay, Sharpe, Fagan, Minnich & McKee, LLP
Seventh Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Family ID: |
26938913 |
Appl. No.: |
10/247797 |
Filed: |
September 19, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60323447 |
Sep 19, 2001 |
|
|
|
Current U.S.
Class: |
315/224 ;
315/209R |
Current CPC
Class: |
H02M 1/32 20130101; Y10S
315/07 20130101; H05B 41/2825 20130101 |
Class at
Publication: |
315/224 ;
315/209.00R |
International
Class: |
H05B 037/02 |
Claims
What is claimed is:
1. A lighting ballast comprising: a voltage source; a switching
portion including first and second complementary transistors for
converting a direct current signal into an alternating current
signal; a drive portion; a resonant load portion for receiving a
lamp; and, a transformer for boosting voltage from the voltage
source to the resonant load portion.
2. The lighting ballast as set forth in claim 1, wherein the
resonant load portion requires a starting voltage of up to 600 V or
more to ignite the lamp.
3. The lighting ballast as set forth in claim 1, wherein the
voltage source supplies between 5 and 7 volts to the ballast.
4. The lighting ballast as set forth in claim 1, wherein the
transformer boosts the voltage from the voltage source to over 1000
V across the resonant load portion during a lamp ignition
period.
5. The lighting ballast as set forth in claim 1, wherein a
potential across the resonant load portion is approximately 50 V
during a steady-state operation period.
6. The lighting ballast as set forth in claim 1, wherein the
transformer includes a primary coil and a secondary coil, the
secondary coil being in operative connection with the resonant load
portion.
7. The lighting ballast as set forth in claim 6, wherein current is
induced in the secondary coil by current passing through the
primary coil, the induced current being controllable by varying a
coil turns ratio of the secondary coil to the primary coil.
8. The lighting ballast as set forth in claim 1, wherein the
transformer is an auto transformer.
9. A method of igniting a lamp comprising: supplying a threshold
voltage across a resonant load portion of a lighting ballast, the
threshold voltage being significantly higher than a voltage from
the voltage source, the voltage from the voltage source being
boosted by a transformer; and, converting direct current from the
voltage source into alternating current by passing the current from
the voltage source through a switching portion, the switching
portion including a first transistor and a second transistor.
10. The method as set forth in claim 9, wherein the threshold
voltage is between 500 and 700 volts, and the voltage source is
between 5 and 7 volts.
11. The method as set forth in claim 9, wherein the transformer
boosts the voltage more in an ignition phase of the ballast than in
a steady state operation phase of the ballast.
12. The method as set forth in claim 9, further including:
controlling a variable tap on a secondary winding of the
transformer, the variable tap being used to vary a turns ratio of
the secondary winding to a primary winding of the transformer.
13. The method as set forth in claim 12, wherein the variable tap
on the secondary winding is used to control an intensity of the
light source during steady-state operation of the light source.
14. A portable lighting ballast comprising: a direct current
battery; a compact fluorescent lamp that requires an alternating
signal of at least 600 volts to ignite; a complementary pair of
MOSFETs that turn a direct current signal from the battery into an
alternating current signal; a resonant inductor winding; a drive
inductor winding that taps power from the resonant inductor
winding; a transformer for boosting voltage to the lamp, the
transformer including: a primary winding that develops a voltage
when subjected to current; a secondary winding that boosts the
voltage across the primary winding, providing a forcing function
that is amplified by a turns ratio of the primary and secondary
windings.
15. The portable lighting ballast as set forth in claim 14, wherein
the battery is one of a 6 volt cell, and multiple cells that equal
6 volts when connected in series.
16. The portable lighting ballast as set forth in claim 14, wherein
the transformer boosts the voltage across the primary winding to
approximately 1200 volts.
17. The portable lighting ballast as set forth in claim 14, wherein
the turns ratio is adjustable in steady-state operation to vary an
intensity of the lamp.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the artificial illumination
arts. It finds particular application in providing high ignition
voltages for portable lamp ballasts and will be described with
particular reference thereto. It is to be appreciated, however,
that the present invention is also applicable to boosting voltages
in fixed ballasts and other circuits, and is not limited to the
aforementioned application.
[0002] Typical portable lamp ballasts utilize relatively low-cost,
low-voltage sources to operate the lamp. For instance, certain
types of popular fluorescent camping lanterns utilize four "D"
cells. In other words, the lantern has a six volt source.
Typically, much larger voltages are needed to ignite and sustain a
lighted fluorescent lamp. Inexpensive fluorescent lamps, as are
commonly found in such lanterns, require on the order of about 200
Volts to ignite. Consequently, when these systems initiate
start-up, extremely high circulating currents are present in
resonant tanks of the ballast, and relatively high-valued circuit
components are required to meet the voltage demands for lamp
ignition.
[0003] In addition to having high startup currents, typical
portable ballasts are inefficient. As a result of limited voltage
available from direct current sources, typical portable lamps
utilize light sources that require less voltage to ignite, but are
more inefficient, lessening light output and battery life.
BRIEF DESCRIPTION OF THE INVENTION
[0004] In accordance with one aspect of the present invention, a
lighting ballast is provided. A voltage source provides current
that is converted by a switching portion, the switching portion
including first and second transistors. A drive portion is
included. A resonant load portion receives a lamp, and a
transformer boosts the voltage from the switching portion to the
resonant load portion.
[0005] In accordance with another aspect of the present invention,
a method of igniting a lamp is included. A threshold voltage is
supplied by boosting a signal significantly higher than its direct
current source. The direct current is converted into alternating
current by a switching portion, the switching portion including
first and second transistors.
[0006] In accordance with another aspect of the present invention,
a portable lamp ballast is provided. A direct current battery
provides power to the ballast. A complementary pair of MOSFETs
convert the direct current signal from the battery into an
alternating current signal. A drive inductor taps power from a
resonant inductor. A transformer including primary and secondary
windings boosts the alternating current signal to the lamp.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention may take form in various components and
arrangements of components, and in various steps and arrangements
of steps. The drawings are only for purposes of illustrating
preferred embodiments and are not to be construed as limiting the
invention.
[0008] FIG. 1 is a circuit diagram of a ballast circuit, in
accordance with the present invention;
[0009] FIG. 2 is a time-voltage graph showing start-up and
steady-state voltages;
[0010] FIG. 3 is a graph showing circuit activity in select
components in time.
DETAILED DESCRIPTION OF THE INVENTION
[0011] With reference to FIG. 1, a lamp 10 is operably connected
between contacts 12, 14 of a ballast housing circuit. In the
preferred embodiment, the circuit is powered by a direct current
(DC) battery 16 of 5 to 7 V. Preferably the bus voltage 16 is
between 5.5 and 6 volts with 6 volts being ideal. The circuit is
referenced at point 18 to ground. The lamp 10 is preferably a
compact fluorescent lamp that operates at a particular frequency or
range of frequencies. The ballast circuit provides AC power at the
operational frequency of the lamp 10.
[0012] In order to convert a DC signal into an AC signal, a first
transistor 20 and a second transistor 22 alternate between periods
of conductivity and periods of non-conductivity, out of phase with
each other. That is, when the first transistor 20 is conductive,
the second transistor 22 is non-conductive, and vice-versa. The
action of alternating periods of conduction of the transistors
provides an AC signal across the contacts 12 and 14. In the
preferred embodiment, the transistors are MOSFETs, but it is to be
understood that bipolar junction transistors or other field effect
transistors are also possible.
[0013] Each transistor 20, 22 has a respective gate and source. The
voltage from gate to source on either transistor defines the
conduction state of that transistor. That is, the gate-to-source
voltage of transistor 20 defines the conductivity of transistor 20
and the gate-to-source voltage of transistor 22 defines the
conductivity of transistor 22. As shown, the sources of the two
transistors 20, 22 are connected at a common node 24. The gates of
the transistors 20, 22 are connected at a control node 26. The
single voltage between the control node 26 and the common node 24
determines the conductivity of both transistors 20, 22. The drains
of the transistors 20, 22 are connected to the bus voltage 16 and
ground 18, respectively.
[0014] A gate drive circuit, connected between the common node 24
and the control node 26 controls the conduction states of the
transistors 20, 22. The gate drive circuit includes a serial
capacitor 27, and a drive inductor 28 that is connected to a
resonant inductor 30 at the common node 24. The other end of the
drive inductor 28 is coupled to a phase inductor 32. The phase
inductor 32 is used to adjust the phase angle of the base-emitter
voltage appearing between nodes 24 and 26. The drive inductor 28
provides a driving energy for the operation of the drive circuit.
The resonant inductor 30 along with a resonant capacitor 33
connected between nodes 12 and 14 determine the operating frequency
of the lamp 10. The serial capacitor 27 charges to provide
sufficient voltage to turn the first transistor 20 conductive.
During steady state operation of the ballast, the serial capacitor
27 aids in switching between the two transistors 20, 22.
[0015] As stated previously, the voltage source is preferably a 6 V
battery, or its equivalent. The lamp 10 of the preferred embodiment
has a threshold ignition voltage of 500 to 700 V, more preferably
in the range of 550 to 650 V with 600 V being most preferred. A
transformer 34 boosts the bus voltage of 6 V to a magnitude
adequate to ignite the lamp 10. Preferably, the transformer 34
boosts the voltage to between 1.0 and 1.4 kV during a period of
time between when the ballast is activated and the lamp 10 ignites.
The preferred ignition voltage is between 1.1 and 1.3 kV with 1.2
kV being ideal. After the lamp ignites, the ballast circuit settles
to a steady state operation mode in which the transformer 34 boosts
the bus voltage to a relatively small steady state value, relative
to the ignition voltage. The steady state value of the preferred
embodiment is on the order of 50 V.
[0016] The transformer 34 includes a primary winding 36 and a
secondary winding 38. Current that passes through the primary
winding 36 induces a current in the secondary winding 38. The
secondary winding 38 is on operative connection with the lamp 10.
The number of coil turns of the secondary winding 38 exposed to
current passing through the primary winding 36 is controllable.
Thus, the magnitude of the voltage transform is controllable. In
the preferred operation of the transformer, during lamp ignition,
all of the windings of the secondary coil 38 are exposed to the
primary coil 36. This boosts the voltage to 1.2 kV, as discussed
previously. Subsequent to lamp ignition, the number of secondary
coil 38 windings exposed to the primary coil 36 is reduced, and the
voltage across the lamp 10 drops to its steady state operating
value. In an alternate embodiment, the transformer 34 is an auto
transformer.
[0017] In the preferred embodiment, during periods of time when the
lamp 10 is lit, a user can manipulate the windings ratio between
the secondary and primary coils 38, 36 to adjust an intensity of
the lamp 10. The user can select high medium and low settings, for
instance, thereby changing the windings ratio, the voltage across
the lamp 10 and ultimately the brightness of the lamp 10. Possible
windings ratios are, for high intensity, 24:1, for medium
intensity, 12:1, and for low intensity, 6:1. Alternately, an analog
dial may be used to select and de-select windings, giving the user
a dimming control of the intensity of the lamp. Regardless of the
method used to give the user intensity control, the lowest setting
that the user may select still provides the lamp 10 with sufficient
voltage to stay lit, unless, of course, if the user selects an off
position, in which power is cut from the ballast circuit.
[0018] Additionally, the ballast circuit includes smoothing
capacitors 40, 42 between the bus voltage 16 and ground 18 to
smooth abnormalities and noise in the bus voltage signal. Starting
resistors 44, 46 prevent current in the ballast circuit from
exceeding tolerable levels during startup, before the capacitors
and inductors are charged. Back to back Zener diodes 48, 50 clamp
the voltage across the transistors 20, 22.
[0019] During lamp ignition, and with reference to FIG. 2, the
ballast circuit boosts the voltage across the lamp 52 to a
temporary ignition voltage 54. With a lamp having a steady state
resistance of 400 .OMEGA., the ballast achieves 1.2 kV with a
battery voltage of 5.5 volts. This ensures sufficient voltage as
the battery discharges. From the time the lamp is switched on (0 s)
to lamp ignition at about 2 ms, the starting voltage of 1.2 kV is
applied. After the lamp ignites, the voltage settles to a steady
state voltage 56 between 40 and 60 volts, with 50 volts being
preferred. The steady state voltage 56 is maintained while the lamp
is in normal operation.
[0020] With reference to FIG. 3, waveforms across select circuit
components are provided over a period of 20 .mu.s. The curve 58
depicts a gate-source voltage of the first and second transistors
20, 22. Only one is shown, but the other transistor has a
gate-source voltage preferably identical, but 180.degree. out of
phase. As is shown, the gate source voltage resembles a square
wave, having transition periods of less than 2 .mu.s, ranging from
approximately 5V to -5V. The source drain voltage of the second
transistor 60 is provided. This square wave function ranges from
about 5.5 to 6 V (bus voltage) down to zero volts. The current
across the phase inductor 62 is provided for comparison. The
current 62 preferably alternates between approximately 5 A and -5
A. The curve 64 is the resultant voltage across the lamp 10, which
is an AC signal.
[0021] Exemplary component values for the circuit of FIG. 1 are as
follows:
1 Part Description Part Number Nominal Value Lamp 10 23 watts DC
Bus Voltage 16 6 Volts Circuit Reference 18 0 Volts Serial
Capacitor 27 47 nanofarads First Transistor 20 IRLML2502 Second
Transistor 22 IRLML6401 Drive Inductor 28 5.6 microhenries Resonant
Inductor 30 560 microhenries Phase Inductor 32 220 microhenries
Resonant Capacitor 33 2.2 nanofarads Primary Winding 36 13.9
microhenries Secondary Winding 38 8 millihenries Smoothing
Capacitor 40 10 microfarads Smoothing Capacitor 42 10 microfarads
Starting Resistor 44 100 k Ohms Starting Resistor 46 3 k Ohms Zener
Diode 48 1N5227 Zener Diode 50 1N5227
[0022] The invention has been described with reference to the
preferred embodiment. Modifications and alterations will occur to
others upon a reading and understanding of the preceding detailed
description. It is intended that the invention be construed as
including all such modifications and alterations insofar as they
come within the scope of the appended claims or the equivalents
thereof.
* * * * *